1. Field of the Invention
The present invention relates to a device for mounting boards, that is used for accommodating circuit boards mounting electronic parts in a housing. More particularly, the invention relates to a device for mounting boards making it possible to decrease the cost and to improve the operation efficiency and reliability.
2. Prior Art
In an electronic control unit for controlling the injection of fuel or for controlling the ignition of, for example, an automotive engine, the circuit board has heretofore been accommodated in a housing in order to protect the electronic parts mounted on the circuit board from the external environment.
For mounting the circuit boards in a casing, furthermore, various board-mounting devices have been proposed for positioning and securing the circuit boards from the standpoint of enhancing the productivity by decreasing the number of steps without using separate securing means such as screws or the like.
FIG. 8 is a side sectional view illustrating a conventional board-mounting device disclosed in Japanese Unexamined Patent Publication No. 177518/1996.
In FIG. 8, a case body 20 constituting a housing includes a back surface plate 20a positioned at the deepest end and side surface plates 20b positioned on both sides.
A board-securing groove 23 of a V-shape in cross section is formed in the inner surface of the back surface plate 20a. Furthermore, a board guide groove 25 of a uniform width is formed in the inner surfaces of the two side surface plates 20b so as to be continuous to the board-securing groove 23.
The case body 20 has a case closure 26 coupled to an open end. A board-securing groove 27 of the same shape as the board-securing groove 23 is formed in the surface of the case closure 26. The board-securing groove 27 is formed to be continuous to the board guide groove 25.
The case closure 26 is secured to the case body 20 via screws 29.
A circuit board 30 is held and secured between the board guide grooves 23 and 27. Both ends of the circuit board 30 are held by the board guide grooves 23 and 27 of a V-shape in the direction of thickness of the circuit board 30, and are positioned and secured.
A plurality of electronic parts 32 are mounted on the circuit board 30 to realize the required functions of the control unit.
The case closure 26 is provided with a connector 33 for connection to an external unit, and a plurality of lead wires 35 of the connector 33 are connected to a pattern on the circuit board 30.
When the case body 20 and the case closure 26 are coupled together, the circuit board 30 is positioned by the guide groove 25 and is secured by the board-securing grooves 23 and 27.
This makes it possible to position and secure the circuit board 30 in the case body 20 and in the case closure 26 without using any separate securing means such as screws.
When the circuit board 30 is positioned and secured between the board guide grooves 23 and 27 as shown in FIG. 8, however, the circuit board 30 must be correctly positioned and inserted in the board guide groove 25 which is relatively narrow having a width equal to the thickness of the circuit board 30, so that the circuit board 30 can be inserted in the case body 20.
Furthermore, the board guide groove 25 is guiding the circuit board 30 in the direction of its thickness only. Therefore, the circuit board 30 may often be incorrectly inserted such as front surface back or front side back.
In order to prevent the circuit board 30 from being erroneously inserted, a special inspection facility is required. In order to inspect modern electronic control units having complex constitution, in particular, a special inspection facility is required such as an image processor for checking.
Moreover, to insert plural pieces of circuit boards in an overlapped manner in the housing, special parts or mechanisms are necessary for supporting and securing the individual circuit boards.
According to the conventional board-mounting device as described above, the circuit board is inserted in the case body 20 via the board guide groove 25, and both ends of the circuit board 30 are held by the board-securing grooves 23 and 27. Therefore, highly precise positioning operation is required impairing the operation efficiency.
Besides, it is not allowed to prevent the circuit board 30 from being erroneously inserted. Therefore, the reliability is low, and a new mechanism is required for preventing the erroneous insertion, resulting in an increase in the cost.
Besides, when plural pieces of circuit boards are to be inserted in an overlapped manner in the case body 20, special parts are needed for supporting and securing the individual circuit boards, resulting in an increase in the cost.